Max engine coolant temp?

[93gmc6.5]

What is the max engine operating coolant temp?
Can I rely on the stock temp gauge or should I put on a aftermarket one?
What temp does a stock fan clutch engage and disengage?

[JCM5]

Typical Diesel should not operate over 240F int.
If you run 220 on a hot 90plus day, this is normal
The cooler 180 - 190 is best running and you will notice a power.
Cooling upgrades? Otherwise go with a hi flow 180 thermostat

[Hubert]

Length of time at elevated temps and how fast it gets there are important.
If towing a hill by the time the coolant is 230F-240F might have cooked pistons already. Exhaust gas temperature should be monitored.

Stock fan locks on at ~ 220-225F ish range I think BUTT the radiator has to saturate at high temp some first - motor will be a little hotter by then.

Diesels like to run hotter best perf is at ~ 195F-205F. But lots like the 180F thermostats. I am running 2. I don't like underhood temps too high. Can contribute to early death of the PMD/FSD depending on mounting location.

OE guage is ok as you don't need to know exactly temp. I say if you want to add a guage get an oil temp guage.